In a charged-particle optical apparatus of the mentioned kind charged particles such as electrons or ions are brought to high kinetic energies, by means of an electro-optical column employing electrostatic high voltages in the range of several kilovolts (kV), and projected onto a target in order to perform certain structuring processes such as CVD processes, electron-based structuring of the target surface and exposure of a resist-layer in order to form a mask for subsequent etching processes. The high voltages used in these apparatuses have to be safely confined so as to avoid electric hazards to the operating personnel as well as surrounding devices. At the same time, it is required to keep the components of the electro-optical column, which includes parts operated at high and low voltages, stably at their respective positions with small tolerances of mutual alignment.
A conventional approach is to keep the entire electro-optical column within one electrostatic housing kept a ground potential (or zero potential, 0 V). For such a setup, it is necessary to provide for high-voltage feedthroughs for the high-voltage supply lines that are used to for high-voltage components, which are bulky and expensive.
Another approach is to employ a high-voltage housing which encases the high-voltage section of the electro-optical column. Then, the insulation between the high-voltage housing and the rest of the electro-optical column at low voltages has to be realized as a rigid device in order to provide for both electric insulation and rigid mechanical connection. However, conventional insulating devices envisaged a massive insulating ring, which involves high mass and costs, has high risk of breakage and is difficult to adjust with regard to the position of high-voltage and low-voltage sections.